Image is human's primary information source, and optical imaging is the primary way to obtain images. An optical imaging system generally consists of an illumination unit and a detection unit. Performing optical imaging on a non-luminous target object by the conventional way is generally to illuminate the object with a stable and uniform illumination light field, and to collect the light reflected from the object surface through some lenses so as to form an image of the target object onto some photosensitive recording medium (such as photographic film, pixelated CCD camera, pixelated CMOS camera, and etc.). The performances of the utilized lens and photosensitive device are main factors to affect imaging quality. The resolution of the resultant images is subject to the pixel pitch of the utilized photosensitive device and the performance of the utilized lens. For higher image resolution, the pixel pitch should be smaller. However, photosensitive devices with small pixel pitch are commonly difficult to be manufactured and might reduce signal-to-noise ratio. Besides, the spectral characteristics of photosensitive device have larger difficulty for some imaging applications beyond visible waveband. For example, the existing CCD, CMOS and other imaging devices based on silicon-based semiconductor have difficulty in working over bands like infrared, terahertz, X-ray, and etc. In the conventional imaging model, only the light that is from target object and transmits through lenses without scattering in transmission from the object to the detector keeps the spatial information of the target object and with such light the image can be formed; however, the light that is scattered in transmission losses the spatial information of the target object has no contribution to imaging but to noise. Therefore, it is challenging to image a target object hidden behind any scattering media (such as, ground glass) by means of the conventional imaging.
Recently, people pay more attention to single-pixel imaging techniques, which has essential difference with conventional imaging techniques in terms of imaging mechanism. The single-pixel imaging techniques potentially allow one to break the limitations of classical imaging model in some special imaging applications. Single-pixel detectors (such as, photodiodes), instead of pixelated cameras, are utilized to collect light signals and computationally reconstruct images. As such, single-pixel imaging is an instance of computational imaging techniques. Contemporary single-pixel imaging techniques originate from ghost imaging which initially utilized quantum entanglement effect. [T. B. Pittman, Optical imaging by means of two-photon quantum entanglement. Physical Review A. 52, R3429 (1995).] And later, it was developed into single-pixel ghost imaging by using thermal light [R. S. Bennink, S. J. Bentley, R. W. Boyd, “Two-Photon” coincidence imaging with a classical source. Physical Review Letters. 89, 113601 (2002)], and single-pixel imaging based on compressed sensing [M. F. Duarte, M. A. Davenport, D. Takhar, J. N. Laska, T. Sun, K. F. Kelly, R. G. Baraniuk, Single-Pixel Imaging via Compressive Sampling. IEEE Signal Processing Magazine. 25, 83-91 (2008)].
Single-pixel imaging has been a hot research topic for over 10 years. However, the imaging quality of single-pixel imaging techniques is hardly comparable to that of existing conventional optical imaging techniques. Due to the probabilistic nature, single-pixel ghost imaging techniques use speckle light fields and compressive sampling based single-pixel imaging techniques use random patterns for illumination. However, neither the speckle patterns nor random patterns have a closed-form expression in mathematics. Such a probabilistic nature also leads to the facts that a great number (millions) of measurements are needed to reconstruct an image, and that the reconstruction result is only an approximation to the true one and the reconstruction quality is not comparable to that by conventional optical imaging techniques.